One of the display systems combining a field sequential display unit and liquid crystal shutter glasses is a three-dimensional display system. FIG. 13 shows an exemplary three-dimensional display system. For example, the three-dimensional system is comprised of a field sequential display unit (liquid crystal display apparatus) 20 and liquid crystal shutter glasses 41. The liquid crystal display apparatus 20 alternately displays right-eye images and left-eye images. The liquid crystal shutter glasses 41 have a right-eye liquid crystal shutter 41a and a left-eye liquid crystal shutter 41b. The right-eye liquid crystal shutter 41a and left-eye liquid crystal shutter 41b are switched between transmission and shielding in sync with the right-eye images and left-eye images displayed on the liquid crystal display apparatus 20. In this figure, the lens in white is in the transmission state and the lens in black is in the shielding state. The right-eye shutter and left-eye shutter are alternately switched to lead the right-eye image and left-eye image on the liquid crystal display apparatus 20 to the right eye and left eye of the observer 42, respectively. The right-eye image and left-eye image displayed on the liquid crystal display apparatus are images on which the parallax between the right and left eyes is reflected so that the observer 42 can view them as three-dimensional images.
Another display system combining a field sequential display unit and liquid crystal shutter glasses is a multiview display system (for example, Patent Literature 1). The multiview display system has the same configuration as the three-dimensional display system shown in FIG. 13. In a multiview system, the liquid crystal display apparatus 20 displays images directed to multiple observers in sequence. The liquid crystal shutter glasses 41 used by the multiple observers repeat transmission/shielding in sync with the corresponding display. This behavior is shown in FIG. 14.
In the example shown in FIG. 14, the liquid crystal display apparatus 20 displays an image A1 to an observer 42a, an image B1 to an observer 42b, an image C1 to an observer 42c, an image A2 to the observer 42a, an image B2 to the observer 42b, an image C2 to the observer 42c, . . . in sequence. The liquid crystal shutter glasses 41 of the observer 42a is in the transmission state when the images A1, A2, . . . are displayed and in the shielding state when the images B1, B2, . . . , C1, C2, . . . are displayed. In this way, observer 42a can continuously observes the images A1, A2, . . . . For the other observers 42b and 42c, the transmission state is created when the corresponding images B1, B2, . . . or C1, C2, . . . are displayed and the shielding state is created when the other images are displayed. In this way, the multiple observers can view different displayed images.
Furthermore, the display unit of a portable information terminal such as a laptop computer can be used as a field sequential display unit and combined with liquid crystal shutter glasses to realize a highly confidential portable information terminal that allows only the user of the liquid crystal shutter glasses to view the information. Such an example is shown in FIG. 15. The field sequential display unit 44 of a portable information terminal 43 alternately displays images and inverted images thereof such as an image A, an inverted image A′ of the image A, an image B, an inverted image B′ of the image B, . . . and displays multiple images A (A′), B (B′), . . . in sequence. In such a case, if the observer observes the display screen without wearing liquid crystal shutter glasses 41, the images A and B are achromatized with their inverted images. Observers without glasses cannot recognize images A and B. However, with the liquid crystal shutter glasses 41 being switched to the transmission state in sync with the display of the images A and B and to the shielding state in sync with their inverted images A′ and B′, observer 42 wearing the liquid crystal shutter glasses 41 can recognize images A and B. Therefore, only observer 42 using the liquid crystal shutter glasses 41 can recognize the display.
In the above described display systems using liquid crystal shutter glasses, the observer may sense flickering due to ambient light because the liquid crystal shutter glasses also transmit/shield the ambient light or light not from the display. Particularly, the observer may sense more flickering under lighting equipment repeating instantaneous blinking such as a fluorescent lamp because the transmission/shielding cycle of the liquid crystal shutter glasses and the lighting cycle of the lighting equipment do not match.
Patent Literature 2 and 3 describe techniques for reducing the flickering in the use of liquid crystal shutter glasses. A three-dimensional image recognition apparatus, described in FIG. 2 of Patent Literature 2, combines a CRT having a linear polarization filter on the display surface with liquid crystal shutter glasses comprising, from the CRT side, a liquid crystal sealing glass plate and a linear polarization filter. In this combination, the display light from the CRT is polarized light. Therefore, the liquid crystal sealing glass plate and linear polarization filter of the liquid crystal shutter glasses transmit or shield the display light. On the other hand, the ambient light (light from any source other than the CRT) is not polarized light and, therefore, is not shielded by the liquid crystal shutter glasses. Consequently, the transmission/shield switching is effective only within the view angle to the CRT display area, reducing the flickering due to ambient light. In Patent Literature 3, FIG. 1 describes a three-dimensional image display apparatus similar to the one in Patent Literature 2. Furthermore, in Patent Literature 3, FIG. 2 describes provision of a liquid crystal cell on the front surface of a color image receiving apparatus and use of polarization glasses as having the same effect as in Patent Literature 2 and Patent Literature 3, FIG. 1.
Patent Literature 4 describes a display system combining a special liquid crystal panel having a display screen visually unrecognizable to the naked eye with a visualizing means having a polarization filter for visualizing the screen of the special liquid crystal panel. One of the visualizing means is glasses having a polarization filter only on a part of the spectacle lens in order to prevent peek through the glasses (Patent Literature 4, FIG. 8). Similarly to Patent Literature 4, Patent Literature 5 to 8 describe glasses having spectacle lenses partly formed by a polarization filter, electronic shutter element, electronic shutter, or liquid crystal light modulation layer. In Patent Literature 5, the polarization glasses for viewing three-dimensional images have a transmission part for easy observation of things other than the displayed image. In Patent Literature 6, the electronic shutter element is embedded in the lens plastic of stereo glasses and the spectacle lens is partly formed by an electronic shutter for improved weather resistance of the electronic shutter element and combined use with vision corrective glasses. In Patent Literature 7, FIG. 1 describes a spectacle lens partly formed by an electronic shutter. In Patent Literature 8 describes a spectacle lens having a liquid crystal light modulation layer in the upper half to cut off strong light and brightness and to easily read characters in a close range.
The Patent Literature referred to in the above are as follows.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI Publication No. 2006-186768 (pages 1 to 3);    Patent Literature 2: Unexamined Japanese Patent Application KOKAI Publication No. 2002-82307 (pages 1-2 and FIGS. 2, 4, and 5);    Patent Literature 3: Unexamined Japanese Patent Application KOKAI Publication No. S62-191819 (pages 1-3 and FIGS. 1 and 2);    Patent Literature 4: Unexamined Japanese Patent Application KOKAI Publication No. 2004-280042 (pages 1-2 and FIGS. 1A, 2A, and 8);    Patent Literature 5: Unexamined Japanese Patent Application KOKAI Publication No. H6-324287 (page 1 and FIG. 2);    Patent Literature 6: Unexamined Japanese Patent Application KOKAI Publication No. S57-188012 (pages 1-3 and FIG. 1);    Patent Literature 7: Unexamined Japanese Patent Application KOKAI Publication No. 2002-116217 (page 3 and FIG. 1); and    Patent Literature 8: Unexamined Japanese Patent Application KOKAI Publication No. H2-308214 (pages 1-2 and FIG. 2).